This heating element control with up to 3 kW was obtained from an old American documentation. SCRs must be load-compliant, and transistors can be current equivalents.
The circuit shown was found in the National Semiconductor's Linear Applications Handbook of 1994....
This circuit from a Popular Electronics shows how to take the audio signal from a telephone line...
This circuit is from a Radio Electronics from April 1972. The circuit uses power transistors of...